Eyesore small yet horrid (4)
I believe the answer is:
stye
'eyesore' is the definition.
(I've seen this before)
'small yet horrid' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'horrid' is an anagram indicator.
'yet' anagrammed gives 'tye'.
's'+'tye'='STYE'
(Other definitions for stye that I've seen before include "Inflamed swelling on the edge of an eyelid" , "swelling by organ" , "Animal pen" , "Red eye" , "makes viewer sore" .)